Eosinophilia is a prominent feature of many diseases including asthma. Recent evidence has shown that the eosinophil, through action of its major basic protein (MBP), is likely to be a significant contributor to airway inflammation in asthma. The eosinophil, like its granulocyte counterpart the neutrophil, will release toxic oxygen products when activated. These products, like the eosinophil MBP, are also capable of causing tissue damage. Studies evaluating eosinophil function have been limited by methods to isolate eosinophils in sufficient purity and number. Thus, we have modified an isolation method with Percoll to allow for eosinophil purification from which sufficient isolates are obtained to evaluate functional activity. The eosinophil, when activated during incubation with particulate (zymosan) or soluble stimuli, will emit light, chemiluminescence, as activated oxygen species are released. In allergic rhinitis, the isolated eosinophil, but not neutrophil, chemiluminescence response is enhanced. Because eosinophil-related tissue damage may be important to the pathogenesis of asthma, we propose to evaluate eosinophil function in asthma. Isolated eosinophils will be obtained from asthma patients and their function will be compared to normal eosinophils and neutrophils by measuring the chemiluminescence response, superoxide release, lysosomal beta-glucuronidase release and chemotaxis. Furthermore, those functions will be evaluated during an asthma attack and compared to the intensity of airway obstruction.